From: Song Liu <songliubraving@fb.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>, Ian Rogers <irogers@google.com>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCHSET v2 0/3] perf stat: Enable BPF counters with --for-each-cgroup
Date: Thu, 17 Jun 2021 06:33:28 +0000 [thread overview]
Message-ID: <55A8ECB0-0299-4A07-B285-E9F0D611E822@fb.com> (raw)
In-Reply-To: <20210616223212.GE4272@worktop.programming.kicks-ass.net>
> On Jun 16, 2021, at 3:32 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Jun 16, 2021 at 09:33:42AM -0700, Namhyung Kim wrote:
>
>>> That seems unfortunate; there's no bpf helper to iterate cgroup
>>> hierarchy?
>>
>> I couldn't find one..
>
> Song, is that something that would make sense to have?
I think we can solve this with bpf_get_current_ancestor_cgroup_id and
a bounded loop. Like:
/* get diff_reading, which is reading - prev_reading */
for (i = 0; i < 10 /* at most 10 levels */; i++) {
__u64 cgroup_id = bpf_get_current_ancestor_cgroup_id(i);
if (!cgroup_id)
break;
/* add diff_reading to cgroup_id */
}
>
>>>> * there's no reliable way to trigger running the BPF program
>>>
>>> You can't attach to the PERF_COUNT_SW_CGROUP_SWITCHES event?
>>
>> I did it. But the BPF test run seems not to work with perf_event.
>> So it needs to trigger a cgroup switch manually..
>
> AFAICT it should be possible to set a bpf prog on a software event.
> perf_event_set_bpf_prog() will take the first branch
> (!perf_event_is_tracing()) and call perf_event_set_bpf_handler().
>
> That should then result in running the bpf program every time the event
> would generate a sample.
>
> So if you configure the event to sample on every single event, it should
> then run your program every time.
>
> This is all from looking at the code, because I really can't operate any
> of that for real. I suspect Song can help out.
>
> The alternative is to attach a BPF program to the sched_switch
> tracepoint and do the cgroup filter in BPF.
We can create a raw_tp BPF program just for BPF_PROG_TEST_RUN (now also called
BPF_PROG_RUN). The program should be the same as current on_switch program.
We don't have to attach the program, just use BPF_PROG_RUN to trigger it.
Would something like this work?
Thanks,
Song
next prev parent reply other threads:[~2021-06-17 6:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-15 1:17 [PATCHSET v2 0/3] perf stat: Enable BPF counters with --for-each-cgroup Namhyung Kim
2021-06-15 1:17 ` [PATCH 1/3] perf tools: Add read_cgroup_id() function Namhyung Kim
2021-06-15 1:17 ` [PATCH 2/3] perf tools: Add cgroup_is_v2() helper Namhyung Kim
2021-06-15 1:17 ` [PATCH 3/3] perf stat: Enable BPF counter with --for-each-cgroup Namhyung Kim
2021-06-16 15:14 ` [PATCHSET v2 0/3] perf stat: Enable BPF counters " Peter Zijlstra
2021-06-16 16:33 ` Namhyung Kim
2021-06-16 22:32 ` Peter Zijlstra
2021-06-17 6:33 ` Song Liu [this message]
2021-06-22 1:43 ` Namhyung Kim
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